Method and device for transmitting/receiving signal of v2x terminal in wireless communication system

ABSTRACT

In one embodiment of the present invention, a method by which a terminal transmits a signal in a wireless communication system comprises the steps of: generating a sequence having a length of 63 and having a punctured central element; inserting one or more zeros among respective elements of the sequence and mapping the sequence to RE; and transmitting the mapped sequence, wherein the number of one or more zeros inserted among the respective elements of the sequence corresponds to (a repetition factor—1), and zeros are additionally inserted such that the sequence is symmetrical with respect to the central element of the sequence, when the repetition factor is an even number.

TECHNICAL FIELD

Following description relates to a wireless communication system, andmore particularly, to a method of generating/mapping/transmitting asequence effective to big frequency offset environment and an apparatustherefor.

BACKGROUND ART

Wireless communication systems have been widely deployed to providevarious types of communication services such as voice or data. Ingeneral, a wireless communication system is a multiple access systemthat supports communication of multiple users by sharing availablesystem resources (a bandwidth, transmission power, etc.) among them. Forexample, multiple access systems include a code division multiple access(CDMA) system, a frequency division multiple access (FDMA) system, atime division multiple access (TDMA) system, an orthogonal frequencydivision multiple access (OFDMA) system, a single carrier frequencydivision multiple access (SC-FDMA) system, and a multi-carrier frequencydivision multiple access (MC-FDMA) system.

Device-to-device (D2D) communication is a communication scheme in whicha direct link is established between user equipments (UEs) and the UEsexchange voice and data directly without an evolved Node B (eNB). D2Dcommunication may cover UE-to-UE communication and peer-to-peercommunication. In addition, D2D communication may be applied tomachine-to-machine (M2M) communication and machine type communication(MTC).

D2D communication is under consideration as a solution to the overheadof an eNB caused by rapidly increasing data traffic. For example, sincedevices exchange data directly with each other without an eNB by D2Dcommunication, compared to legacy wireless communication, networkoverhead may be reduced. Further, it is expected that the introductionof D2D communication will reduce procedures of an eNB, reduce the powerconsumption of devices participating in D2D communication, increase datatransmission rates, increase the accommodation capability of a network,distribute load, and extend cell coverage.

At present, vehicle-to-everything (V2X) communication in conjunctionwith D2D communication is under consideration. In concept, V2Xcommunication covers vehicle-to-vehicle (V2V) communication,vehicle-to-pedestrian (V2P) communication for communication between avehicle and a different kind of terminal, and vehicle-to-infrastructure(V2I) communication for communication between a vehicle and a roadsideunit (RSU).

DISCLOSURE OF THE INVENTION Technical Task

A technical task of the present invention is to provide a method ofgenerating/mapping/transmitting a synchronization signal in environmentwhere a frequency offset is big.

Technical tasks obtainable from the present invention are non-limited bythe above-mentioned technical task. And, other unmentioned technicaltasks can be clearly understood from the following description by thosehaving ordinary skill in the technical field to which the presentinvention pertains.

Technical Solution

To achieve these and other advantages and in accordance with the purposeof the present invention, as embodied and broadly described, accordingto one embodiment, a method of transmitting a signal, which istransmitted by a user equipment (UE) in a wireless communication system,includes the steps of generating a sequence of a length of 63 of whichthe center element of the sequence is punctured, inserting one or more0s between elements of the sequence and mapping the sequence to an RE,and transmitting the mapped sequence. In this case, the number of theone or more 0s inserted between the elements of the sequence correspondsto (repetition factor−1) and if the repetition factor corresponds to aneven number, 0s can be additionally inserted to make symmetry on thebasis of the center element of the sequence.

To further achieve these and other advantages and in accordance with thepurpose of the present invention, according to a different embodiment, auser equipment (UE) transmitting a signal in a wireless communicationsystem includes a transmitter and a receiver, and a processor, theprocessor configured to insert one or more 0s between elements of asequence and map the sequence to an RE, the processor configured totransmit the mapped sequence. In this case, the number of the one ormore 0s inserted between the elements of the sequence corresponds to(repetition factor—1) and if the repetition factor corresponds to aneven number, 0s can be additionally inserted to make symmetry on thebasis of the center element of the sequence.

The number of additionally inserted 0s may correspond to (repetitionfactor—1).

0s can be additionally inserted to make symmetry on the basis of thecenter element of the sequence even when the repetition factorcorresponds to an odd number.

The sequence may indicate that a UE, which has transmitted the sequence,corresponds to an LTE UE.

The sequence can enable a V2X UE, which has received the sequence, toobtain synchronization.

The sequence may correspond to either a Zadoff-Chu sequence or anm-sequence.

The repetition factor may vary depending on whether the sequencecorresponds to the Zadoff-Chu sequence or the m-sequence.

The repetition factor may be proportional to a moving speed of the UE.

The repetition factor can be configured by an RSU.

The repetition factor can be configured according to a frequency of acarrier on which the sequence is transmitted.

The repetition factor can be configured according to whether or not a UEreceiving the sequence is connected to a GPS.

Advantageous Effects

According to the present invention, it is able to efficiently obtainsynchronization even when a frequency offset is big.

Effects obtainable from the present invention are non-limited by theabove mentioned effect. And, other unmentioned effects can be clearlyunderstood from the following description by those having ordinary skillin the technical field to which the present invention pertains.

DESCRIPTION OF DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate embodiments of the invention andtogether with the description serve to explain the principles of theinvention.

FIG. 1 is a diagram for a structure of a radio frame;

FIG. 2 is a diagram for a resource grid in a downlink slot;

FIG. 3 is a diagram for a structure of a downlink subframe;

FIG. 4 is a diagram for a structure of an uplink subframe;

FIG. 5 is a diagram for a configuration of a wireless communicationsystem having multiple antennas;

FIG. 6 is a diagram for a subframe in which a D2D synchronization signalis transmitted;

FIG. 7 is a diagram for explaining relay of a D2D signal;

FIG. 8 is a diagram for an example of a D2D resource pool for performingD2D communication;

FIG. 9 is a diagram for explaining an SA period;

FIGS. 10 to 14 are diagrams for explaining a method ofgenerating/mapping a sequence according to each of embodiments of thepresent invention;

FIG. 15 is a diagram for configurations of a transmitter and a receiver.

BEST MODE Mode for Invention

The embodiments of the present invention described hereinbelow arecombinations of elements and features of the present invention. Theelements or features may be considered selective unless otherwisementioned. Each element or feature may be practiced without beingcombined with other elements or features. Further, an embodiment of thepresent invention may be constructed by combining parts of the elementsand/or features. Operation orders described in embodiments of thepresent invention may be rearranged. Some constructions or features ofany one embodiment may be included in another embodiment and may bereplaced with corresponding constructions or features of anotherembodiment.

In the embodiments of the present invention, a description is made,centering on a data transmission and reception relationship between aBase Station (BS) and a User Equipment (UE). The BS is a terminal nodeof a network, which communicates directly with a UE. In some cases, aspecific operation described as performed by the BS may be performed byan upper node of the BS.

Namely, it is apparent that, in a network comprised of a plurality ofnetwork nodes including a BS, various operations performed forcommunication with a UE may be performed by the BS or network nodesother than the BS. The term ‘BS’ may be replaced with the term ‘fixedstation’, ‘Node B’, ‘evolved Node B (eNode B or eNB)’, ‘Access Point(AP)’, etc. The term ‘relay’ may be replaced with the term ‘Relay Node(RN)’ or ‘Relay Station (RS)’. The term ‘terminal’ may be replaced withthe term ‘UE’, ‘Mobile Station (MS)’, ‘Mobile Subscriber Station (MSS)’,‘Subscriber Station (SS)’, etc.

The term “cell”, as used herein, may be applied to transmission andreception points such as a base station (eNB), sector, remote radio head(RRH) and relay, and may also be extensively used by a specifictransmission/reception point to distinguish between component carriers.

Specific terms used for the embodiments of the present invention areprovided to help the understanding of the present invention. Thesespecific terms may be replaced with other terms within the scope andspirit of the present invention.

In some cases, to prevent the concept of the present invention frombeing ambiguous, structures and apparatuses of the known art will beomitted, or will be shown in the form of a block diagram based on mainfunctions of each structure and apparatus. Also, wherever possible, thesame reference numbers will be used throughout the drawings and thespecification to refer to the same or like parts.

The embodiments of the present invention can be supported by standarddocuments disclosed for at least one of wireless access systems,Institute of Electrical and Electronics Engineers (IEEE) 802, 3rdGeneration Partnership Project (3GPP), 3GPP Long Term Evolution (3GPPLTE), LTE-Advanced (LTE-A), and 3GPP2. Steps or parts that are notdescribed to clarify the technical features of the present invention canbe supported by those documents. Further, all terms as set forth hereincan be explained by the standard documents.

Techniques described herein can be used in various wireless accesssystems such as Code Division Multiple Access (CDMA), Frequency DivisionMultiple Access (FDMA), Time Division Multiple Access (TDMA), OrthogonalFrequency Division Multiple Access (OFDMA), Single Carrier-FrequencyDivision Multiple Access (SC-FDMA), etc. CDMA may be implemented as aradio technology such as Universal Terrestrial Radio Access (UTRA) orCDMA2000. TDMA may be implemented as a radio technology such as GlobalSystem for Mobile communications (GSM)/General Packet Radio Service(GPRS)/Enhanced Data Rates for GSM Evolution (EDGE). OFDMA may beimplemented as a radio technology such as IEEE 802.11 (Wi-Fi), IEEE802.16 (WiMAX), IEEE 802.20, Evolved-UTRA (E-UTRA) etc. UTRA is a partof Universal Mobile Telecommunications System (UMTS). 3GPP LTE is a partof Evolved UMTS (E-UMTS) using E-UTRA. 3GPP LTE employs OFDMA fordownlink and SC-FDMA for uplink. LTE-A is an evolution of 3GPP LTE.WiMAX can be described by the IEEE 802.16e standard (WirelessMetropolitan Area Network (WirelessMAN)-OFDMA Reference System) and theIEEE 802.16m standard (WirelessMAN-OFDMA Advanced System). For clarity,this application focuses on the 3GPP LTE and LTE-A systems. However, thetechnical features of the present invention are not limited thereto.

LTE/LTE-A Resource Structure/Channel

With reference to FIG. 1, the structure of a radio frame will bedescribed below.

In a cellular Orthogonal Frequency Division Multiplexing (OFDM) wirelessPacket communication system, uplink and/or downlink data Packets aretransmitted in subframes. One subframe is defined as a predeterminedtime period including a plurality of OFDM symbols. The 3GPP LTE standardsupports a type-1 radio frame structure applicable to Frequency DivisionDuplex (FDD) and a type-2 radio frame structure applicable to TimeDivision Duplex (TDD).

FIG. 1(a) illustrates the type-1 radio frame structure. A downlink radioframe is divided into 10 subframes. Each subframe is further dividedinto two slots in the time domain. A unit time during which one subframeis transmitted is defined as a Transmission Time Interval (TTI). Forexample, one subframe may be 1 ms in duration and one slot may be 0.5 msin duration. A slot includes a plurality of OFDM symbols in the timedomain and a plurality of Resource Blocks (RBs) in the frequency domain.Because the 3GPP LTE system adopts OFDMA for downlink, an OFDM symbolrepresents one symbol period. An OFDM symbol may be referred to as anSC-FDMA symbol or symbol period. An RB is a resource allocation unitincluding a plurality of contiguous subcarriers in a slot.

The number of OFDM symbols in one slot may vary depending on a CyclicPrefix (CP) configuration. There are two types of CPs: extended CP andnormal CP. In the case of the normal CP, one slot includes 7 OFDMsymbols. In the case of the extended CP, the length of one OFDM symbolis increased and thus the number of OFDM symbols in a slot is smallerthan in the case of the normal CP. Thus when the extended CP is used,for example, 6 OFDM symbols may be included in one slot. If channelstate gets poor, for example, during fast movement of a UE, the extendedCP may be used to further decrease Inter-Symbol Interference (ISI).

In the case of the normal CP, one subframe includes 14 OFDM symbolsbecause one slot includes 7 OFDM symbols. The first two or three OFDMsymbols of each subframe may be allocated to a Physical Downlink ControlCHannel (PDCCH) and the other OFDM symbols may be allocated to aPhysical Downlink Shared Channel (PDSCH).

FIG. 1(b) illustrates the type-2 radio frame structure. A type-2 radioframe includes two half frames, each having 5 subframes, a DownlinkPilot Time Slot (DwPTS), a Guard Period (GP), and an Uplink Pilot TimeSlot (UpPTS). Each subframe is divided into two slots. The DwPTS is usedfor initial cell search, synchronization, or channel estimation at a UE.The UpPTS is used for channel estimation and acquisition of uplinktransmission synchronization to a UE at an eNB. The GP is a periodbetween an uplink and a downlink, which eliminates uplink interferencecaused by multipath delay of a downlink signal. One subframe includestwo slots irrespective of the type of a radio frame.

The above-described radio frame structures are purely exemplary and thusit is to be noted that the number of subframes in a radio frame, thenumber of slots in a subframe, or the number of symbols in a slot mayvary.

FIG. 2 illustrates the structure of a downlink resource grid for theduration of one downlink slot. A downlink slot includes 7 OFDM symbolsin the time domain and an RB includes 12 subcarriers in the frequencydomain, which does not limit the scope and spirit of the presentinvention. For example, a downlink slot may include 7 OFDM symbols inthe case of the normal CP, whereas a downlink slot may include 6 OFDMsymbols in the case of the extended CP. Each element of the resourcegrid is referred to as a Resource Element (RE). An RB includes 12×7 REs.The number of RBs in a downlink slot, NDL depends on a downlinktransmission bandwidth. An uplink slot may have the same structure as adownlink slot.

FIG. 3 illustrates the structure of a downlink subframe. Up to threeOFDM symbols at the start of the first slot in a downlink subframe areused for a control region to which control channels are allocated andthe other OFDM symbols of the downlink subframe are used for a dataregion to which a PDSCH is allocated. Downlink control channels used inthe 3GPP LTE system include a Physical Control Format Indicator CHannel(PCFICH), a Physical Downlink Control CHannel (PDCCH), and a PhysicalHybrid automatic repeat request (HARQ) Indicator CHannel (PHICH). ThePCFICH is located in the first OFDM symbol of a subframe, carryinginformation about the number of OFDM symbols used for transmission ofcontrol channels in the subframe. The PHICH delivers an HARQACKnowledgment/Negative ACKnowledgment (ACK/NACK) signal in response toan uplink transmission. Control information carried on the PDCCH iscalled Downlink Control Information (DCI). The DCI transports uplink ordownlink scheduling information, or uplink transmission power controlcommands for UE groups. The PDCCH delivers information about resourceallocation and a transport format for a Downlink Shared CHannel(DL-SCH), resource allocation information about an Uplink Shared CHannel(UL-SCH), paging information of a Paging CHannel (PCH), systeminformation on the DL-SCH, information about resource allocation for ahigher-layer control message such as a Random Access Responsetransmitted on the PDSCH, a set of transmission power control commandsfor individual UEs of a UE group, transmission power controlinformation, Voice Over Internet Protocol (VoIP) activation information,etc. A plurality of PDCCHs may be transmitted in the control region. AUE may monitor a plurality of PDCCHs. A PDCCH is formed by aggregatingone or more consecutive Control Channel Elements (CCEs). A CCE is alogical allocation unit used to provide a PDCCH at a coding rate basedon the state of a radio channel. A CCE includes a plurality of REgroups. The format of a PDCCH and the number of available bits for thePDCCH are determined according to the correlation between the number ofCCEs and a coding rate provided by the CCEs. An eNB determines the PDCCHformat according to DCI transmitted to a UE and adds a Cyclic RedundancyCheck (CRC) to control information. The CRC is masked by an Identifier(ID) known as a Radio Network Temporary Identifier (RNTI) according tothe owner or usage of the PDCCH. If the PDCCH is directed to a specificUE, its CRC may be masked by a cell-RNTI (C-RNTI) of the UE. If thePDCCH is for a paging message, the CRC of the PDCCH may be masked by aPaging Indicator Identifier (P-RNTI). If the PDCCH carries systeminformation, particularly, a System Information Block (SIB), its CRC maybe masked by a system information ID and a System Information RNTI(SI-RNTI). To indicate that the PDCCH carries a Random Access Responsein response to a Random Access Preamble transmitted by a UE, its CRC maybe masked by a Random Access-RNTI (RA-RNTI).

FIG. 4 illustrates the structure of an uplink subframe. An uplinksubframe may be divided into a control region and a data region in thefrequency domain. A Physical Uplink Control CHannel (PUCCH) carryinguplink control information is allocated to the control region and aPhysical Uplink Shared Channel (PUSCH) carrying user data is allocatedto the data region. To maintain the property of a single carrier, a UEdoes not transmit a PUSCH and a PUCCH simultaneously. A PUCCH for a UEis allocated to an RB pair in a subframe. The RBs of the RB pair occupydifferent subcarriers in two slots. Thus it is said that the RB pairallocated to the PUCCH is frequency-hopped over a slot boundary.

Reference Signals (RSs)

In a wireless communication system, a Packet is transmitted on a radiochannel. In view of the nature of the radio channel, the Packet may bedistorted during the transmission. To receive the signal successfully, areceiver should compensate for the distortion of the received signalusing channel information. Generally, to enable the receiver to acquirethe channel information, a transmitter transmits a signal known to boththe transmitter and the receiver and the receiver acquires knowledge ofchannel information based on the distortion of the signal received onthe radio channel. This signal is called a pilot signal or an RS.

In the case of data transmission and reception through multipleantennas, knowledge of channel states between Transmission (Tx) antennasand Reception (Rx) antennas is required for successful signal reception.Accordingly, an RS should be transmitted through each Tx antenna.

RSs may be divided into downlink RSs and uplink RSs. In the current LTEsystem, the uplink RSs include:

i) DeModulation-Reference Signal (DM-RS) used for channel estimation forcoherent demodulation of information delivered on a PUSCH and a PUCCH;and

ii) Sounding Reference Signal (SRS) used for an eNB or a network tomeasure the quality of an uplink channel in a different frequency.

The downlink RSs are categorized into:

i) Cell-specific Reference Signal (CRS) shared among all UEs of a cell;

ii) UE-specific RS dedicated to a specific UE;

iii) DM-RS used for coherent demodulation of a PDSCH, when the PDSCH istransmitted;

iv) Channel State Information-Reference Signal (CSI-RS) carrying CSI,when downlink DM-RSs are transmitted;

v) Multimedia Broadcast Single Frequency Network (MBSFN) RS used forcoherent demodulation of a signal transmitted in MBSFN mode; and

vi) positioning RS used to estimate geographical position informationabout a UE.

RSs may also be divided into two types according to their purposes: RSfor channel information acquisition and RS for data demodulation. Sinceits purpose lies in that a UE acquires downlink channel information, theformer should be transmitted in a broad band and received even by a UEthat does not receive downlink data in a specific subframe. This RS isalso used in a situation like handover. The latter is an RS that an eNBtransmits along with downlink data in specific resources. A UE candemodulate the data by measuring a channel using the RS. This RS shouldbe transmitted in a data transmission area.

Modeling of MIMO System

FIG. 5 is a diagram illustrating a configuration of a wirelesscommunication system having multiple antennas.

As shown in FIG. 5(a), if the number of transmit antennas is increasedto NT and the number of receive antennas is increased to NR, atheoretical channel transmission capacity is increased in proportion tothe number of antennas, unlike the case where a plurality of antennas isused in only a transmitter or a receiver. Accordingly, it is possible toimprove a transfer rate and to remarkably improve frequency efficiency.As the channel transmission capacity is increased, the transfer rate maybe theoretically increased by a product of a maximum transfer rate Roupon utilization of a single antenna and a rate increase ratio Ri.

R _(i)=min(N _(T) ,N _(R))  [Equation 1]

For instance, in an MIMO communication system, which uses 4 transmitantennas and 4 receive antennas, a transmission rate 4 times higher thanthat of a single antenna system can be obtained. Since this theoreticalcapacity increase of the MIMO system has been proved in the middle of90's, many ongoing efforts are made to various techniques tosubstantially improve a data transmission rate. In addition, thesetechniques are already adopted in part as standards for various wirelesscommunications such as 3G mobile communication, next generation wirelessLAN and the like.

The trends for the MIMO relevant studies are explained as follows. Firstof all, many ongoing efforts are made in various aspects to develop andresearch information theory study relevant to MIMO communicationcapacity calculations and the like in various channel configurations andmultiple access environments, radio channel measurement and modelderivation study for MIMO systems, spatiotemporal signal processingtechnique study for transmission reliability enhancement andtransmission rate improvement and the like.

In order to explain a communicating method in an MIMO system in detail,mathematical modeling can be represented as follows. It is assumed thatthere are NT transmit antennas and NR receive antennas.

Regarding a transmitted signal, if there are NT transmit antennas, themaximum number of pieces of information that can be transmitted is NT.Hence, the transmission information can be represented as shown inEquation 2.

S=└S ₁ ,S ₂ , . . . ,S _(N) _(T) ┘^(T)  [Equation 2]

Meanwhile, transmit powers can be set different from each other forindividual pieces of transmission information S₁, S₂, . . . , S_(N) _(T), respectively. If the transmit powers are set to P₁, P₂, Λ, P_(N) _(T), respectively, the transmission information with adjusted transmitpowers can be represented as Equation 3.

$\begin{matrix}{\hat{s} = {\left\lbrack {{\hat{s}}_{1},{\hat{s}}_{2},\ldots \mspace{14mu},{\hat{s}}_{N_{T}}} \right\rbrack^{T} = \left\lbrack {{P_{1}s_{1}},{P_{2}s_{2}},\ldots \mspace{14mu},{P_{N_{T}}s_{N_{T}}}} \right\rbrack^{T}}} & \left\lbrack {{Equation}\mspace{14mu} 3} \right\rbrack\end{matrix}$

In addition, Ŝ can be represented as Equation 4 using diagonal matrix Pof the transmission power.

$\begin{matrix}{\hat{s} = {{\begin{bmatrix}P_{1} & \; & \; & 0 \\\; & P_{2} & \; & \; \\\; & \; & \ddots & \; \\0 & \; & \; & P_{N_{T}}\end{bmatrix}\begin{bmatrix}s_{1} \\s_{2} \\\vdots \\s_{N_{T}}\end{bmatrix}} = {Ps}}} & \left\lbrack {{Equation}\mspace{14mu} 4} \right\rbrack\end{matrix}$

Assuming a case of configuring NT transmitted signals x₁, x₂, . . . ,x_(N) _(T) , which are actually transmitted, by applying weight matrix Wto the information vector Ŝ having the adjusted transmit powers, theweight matrix W serves to appropriately distribute the transmissioninformation to each antenna according to a transport channel state. x₁,x₂, . . . , x_(N) _(T) can be expressed by using the vector x asfollows.

$\begin{matrix}{x = {\left\lbrack \begin{matrix}x_{1} \\x_{2} \\\vdots \\x_{i} \\\vdots \\x_{N_{T}}\end{matrix} \right\rbrack = {{\begin{bmatrix}w_{11} & w_{12} & \ldots & w_{1\; N_{T}} \\w_{21} & w_{22} & \ldots & w_{2\; N_{T}} \\\vdots & \; & \ddots & \; \\w_{i\; 1} & w_{i\; 2} & \ldots & w_{i\; N_{T}} \\\vdots & \; & \ddots & \; \\w_{N_{T}1} & w_{N_{T}2} & \ldots & w_{N_{T}N_{T}}\end{bmatrix}\begin{bmatrix}{\hat{s}}_{1} \\{\hat{s}}_{2} \\\vdots \\{\hat{s}}_{j} \\\vdots \\{\hat{s}}_{N_{T}}\end{bmatrix}} = {{W\hat{s}} = {WPs}}}}} & \left\lbrack {{Equation}\mspace{14mu} 5} \right\rbrack\end{matrix}$

In Equation 5, w_(ij) denotes a weight between an i^(th) transmitantenna and j^(th) information. W is also called a precoding matrix.

If the NR receive antennas are present, respective received signals y₁,y₂ . . . , y_(N) _(R) of the antennas can be expressed as follows.

y=[y ₁ ,y ₂ . . . ,y _(N) _(R) ]^(T)  [Equation 6]

If channels are modeled in the MIMO wireless communication system, thechannels may be distinguished according to transmit/receive antennaindexes. A channel from the transmit antenna j to the receive antenna iis denoted by h_(ij). In h_(ij), it is noted that the indexes of thereceive antennas precede the indexes of the transmit antennas in view ofthe order of indexes.

FIG. 5(b) is a diagram illustrating channels from the NT transmitantennas to the receive antenna i. The channels may be combined andexpressed in the form of a vector and a matrix. In FIG. 5(b), thechannels from the NT transmit antennas to the receive antenna i can beexpressed as follows.

h _(i) ^(T) =[h _(i1) ,h _(i2) , . . . ,h _(iN) _(T) ]  [Equation 7]

Accordingly, all channels from the NT transmit antennas to the NRreceive antennas can be expressed as follows.

$\begin{matrix}{H = {\begin{bmatrix}h_{1}^{T} \\h_{2}^{T} \\\vdots \\h_{i}^{T} \\\vdots \\h_{N_{R}}^{T}\end{bmatrix} = \begin{bmatrix}h_{11} & h_{12} & \ldots & h_{1\; N_{T}} \\h_{21} & h_{22} & \ldots & h_{2\; N_{T}} \\\vdots & \; & \ddots & \; \\h_{i\; 1} & h_{i\; 2} & \ldots & h_{i\; N_{T}} \\\vdots & \; & \ddots & \; \\h_{N_{R}1} & h_{N_{R}2} & \ldots & h_{N_{R}N_{T}}\end{bmatrix}}} & \left\lbrack {{Equation}\mspace{14mu} 8} \right\rbrack\end{matrix}$

An AWGN (Additive White Gaussian Noise) is added to the actual channelsafter a channel matrix H. The AWGN n₁, n₂, . . . , n_(N) _(R)respectively added to the NR receive antennas can be expressed asfollows.

n=[n ₁ ,n ₂ , . . . ,n _(N) _(R) ]^(T)  [Equation 9]

Through the above-described mathematical modeling, the received signalscan be expressed as follows.

$\begin{matrix}{y = {\begin{bmatrix}y_{1} \\y_{2} \\\vdots \\y_{i} \\\vdots \\y_{N_{R}}\end{bmatrix} = {{{\begin{bmatrix}h_{11} & h_{12} & \ldots & h_{1\; N_{T}} \\h_{21} & h_{22} & \ldots & h_{2\; N_{T}} \\\vdots & \; & \ddots & \; \\h_{i\; 1} & h_{i\; 2} & \ldots & h_{i\; N_{T}} \\\vdots & \; & \ddots & \; \\h_{N_{R}1} & h_{N_{R}2} & \ldots & h_{N_{R}N_{T}}\end{bmatrix}\begin{bmatrix}x_{1} \\x_{2} \\\vdots \\x_{j} \\\vdots \\x_{N_{T}}\end{bmatrix}} + \begin{bmatrix}n_{1} \\n_{2} \\\vdots \\n_{i} \\\vdots \\n_{N_{R}}\end{bmatrix}} = {{Hx} + n}}}} & \left\lbrack {{Equation}\mspace{14mu} 10} \right\rbrack\end{matrix}$

Meanwhile, the number of rows and columns of the channel matrix Hindicating the channel state is determined by the number of transmit andreceive antennas. The number of rows of the channel matrix H is equal tothe number NR of receive antennas and the number of columns thereof isequal to the number NR of transmit antennas. That is, the channel matrixH is an NR×NT matrix.

The rank of the matrix is defined by the smaller of the number of rowsand the number of columns, which are independent from each other.Accordingly, the rank of the matrix is not greater than the number ofrows or columns. The rank rank(H) of the channel matrix H is restrictedas follows.

rank(H)≤min(N _(T) ,N _(R))  [Equation 11]

Additionally, the rank of a matrix can also be defined as the number ofnon-zero Eigen values when the matrix is Eigen-value-decomposed.Similarly, the rank of a matrix can be defined as the number of non-zerosingular values when the matrix is singular-value-decomposed.Accordingly, the physical meaning of the rank of a channel matrix can bethe maximum number of channels through which different pieces ofinformation can be transmitted.

In the description of the present document, ‘rank’ for MIMO transmissionindicates the number of paths capable of sending signals independentlyon specific time and frequency resources and ‘number of layers’indicates the number of signal streams transmitted through therespective paths. Generally, since a transmitting end transmits thenumber of layers corresponding to the rank number, one rank has the samemeaning of the layer number unless mentioned specially.

Synchronization Acquisition of D2D UE

Now, a description will be given of synchronization acquisition betweenUEs in D2D communication based on the foregoing description in thecontext of the legacy LTE/LTE-A system. In an OFDM system, iftime/frequency synchronization is not acquired, the resulting Inter-CellInterference (ICI) may make it impossible to multiplex different UEs inan OFDM signal. If each individual D2D UE acquires synchronization bytransmitting and receiving a synchronization signal directly, this isinefficient. In a distributed node system such as a D2D communicationsystem, therefore, a specific node may transmit a representativesynchronization signal and the other UEs may acquire synchronizationusing the representative synchronization signal. In other words, somenodes (which may be an eNB, a UE, and a Synchronization Reference Node(SRN, also referred to as a synchronization source)) may transmit a D2DSynchronization Signal (D2DSS) and the remaining UEs may transmit andreceive signals in synchronization with the D2DSS.

D2DSSs may include a Primary D2DSS (PD2DSS) or a Primary SidelinkSynchronization Signal (PSSS) and a Secondary D2DSS (SD2DSS) or aSecondary Sidelink Synchronization Signal (SSSS). The PD2DSS may beconfigured to have a similar/modified/repeated structure of a Zadoff-chusequence of a predetermined length or a Primary Synchronization Signal(PSS). Unlike a DL PSS, the PD2DSS may use a different Zadoff-chu rootindex (e.g., 26, 37). And, the SD2DSS may be configured to have asimilar/modified/repeated structure of an M-sequence or a SecondarySynchronization Signal (SSS). If UEs synchronize their timing with aneNB, the eNB serves as an SRN and the D2DSS is a PSS/SSS. Unlike PSS/SSSof DL, the PD2DSS/SD2DSS follows UL subcarrier mapping scheme. FIG. 6shows a subframe in which a D2D synchronization signal is transmitted. APhysical D2D Synchronization Channel (PD2DSCH) may be a (broadcast)channel carrying basic (system) information that a UE should firstobtain before D2D signal transmission and reception (e.g., D2DSS-relatedinformation, a Duplex Mode (DM), a TDD UL/DL configuration, a resourcepool-related information, the type of an application related to theD2DSS, etc.). The PD2DSCH may be transmitted in the same subframe as theD2DSS or in a subframe subsequent to the frame carrying the D2DSS. ADMRS can be used to demodulate the PD2DSCH.

The SRN may be a node that transmits a D2DSS and a PD2DSCH. The D2DSSmay be a specific sequence and the PD2DSCH may be a sequencerepresenting specific information or a codeword produced bypredetermined channel coding. The SRN may be an eNB or a specific D2DUE. In the case of partial network coverage or out of network coverage,the SRN may be a UE.

In a situation illustrated in FIG. 7, a D2DSS may be relayed for D2Dcommunication with an out-of-coverage UE. The D2DSS may be relayed overmultiple hops. The following description is given with the appreciationthat relay of an SS covers transmission of a D2DSS in a separate formataccording to a SS reception time as well as direct Amplify-and-Forward(AF)-relay of an SS transmitted by an eNB. As the D2DSS is relayed, anin-coverage UE may communicate directly with an out-of-coverage UE.

D2D Resource Pool

FIG. 8 shows an example of a UE1, a UE2 and a resource pool used by theUE1 and the UE2 performing D2D communication. In FIG. 8 (a), a UEcorresponds to a terminal or such a network device as an eNBtransmitting and receiving a signal according to a D2D communicationscheme. A UE selects a resource unit corresponding to a specificresource from a resource pool corresponding to a set of resources andthe UE transmits a D2D signal using the selected resource unit. A UE2corresponding to a reception UE receives a configuration of a resourcepool in which the UE1 is able to transmit a signal and detects a signalof the UE1 in the resource pool. In this case, if the UE1 is located atthe inside of coverage of an eNB, the eNB can inform the UE1 of theresource pool. If the UE1 is located at the outside of coverage of theeNB, the resource pool can be informed by a different UE or can bedetermined by a predetermined resource. In general, a resource poolincludes a plurality of resource units. A UE selects one or moreresource units from among a plurality of the resource units and may beable to use the selected resource unit(s) for D2D signal transmission.FIG. 8 (b) shows an example of configuring a resource unit. Referring toFIG. 8 (b), the entire frequency resources are divided into the N_(F)number of resource units and the entire time resources are divided intothe N_(T) number of resource units. In particular, it is able to defineN_(F)*N_(T) number of resource units in total. In particular, a resourcepool can be repeated with a period of N_(T) subframes. Specifically, asshown in FIG. 8, one resource unit may periodically and repeatedlyappear. Or, an index of a physical resource unit to which a logicalresource unit is mapped may change with a predetermined patternaccording to time to obtain a diversity gain in time domain and/orfrequency domain. In this resource unit structure, a resource pool maycorrespond to a set of resource units capable of being used by a UEintending to transmit a D2D signal.

A resource pool can be classified into various types. First of all, theresource pool can be classified according to contents of a D2D signaltransmitted via each resource pool. For example, the contents of the D2Dsignal can be classified into various signals and a separate resourcepool can be configured according to each of the contents. The contentsof the D2D signal may include SA (scheduling assignment), a D2D datachannel, and a discovery channel. The SA may correspond to a signalincluding information on a resource position of a D2D data channel,information on MCS (modulation and coding scheme) necessary formodulating and demodulating a data channel, information on a MIMOtransmission scheme, information on TA (timing advance), and the like.The SA signal can be transmitted on an identical resource unit in amanner of being multiplexed with D2D data. In this case, an SA resourcepool may correspond to a pool of resources that an SA and D2D data aretransmitted in a manner of being multiplexed. The SA signal can also bereferred to as a D2D control channel or a PSCCH (physical sidelinkcontrol channel). The D2D data channel (or, PSSCH (physical sidelinkshared channel)) corresponds to a resource pool used by a transmissionUE to transmit user data. If an SA and a D2D data are transmitted in amanner of being multiplexed in an identical resource unit, D2D datachannel except SA information can be transmitted only in a resource poolfor the D2D data channel. In other word, resource elements (REs), whichare used to transmit SA information in a specific resource unit of an SAresource pool, can also be used for transmitting D2D data in a D2D datachannel resource pool. The discovery channel may correspond to aresource pool for a message that enables a neighboring UE to discovertransmission UE transmitting information such as ID of the UE, and thelike.

Although contents of D2D signal are identical to each other, it may usea different resource pool according to a transmission/receptionattribute of the D2D signal. For example, in case of the same D2D datachannel or the same discovery message, the D2D data channel or thediscovery signal can be classified into a different resource poolaccording to a transmission timing determination scheme (e.g., whether aD2D signal is transmitted at the time of receiving a synchronizationreference signal or the timing to which a prescribed timing advance isadded) of a D2D signal, a resource allocation scheme (e.g., whether atransmission resource of an individual signal is designated by an eNB oran individual transmission UE selects an individual signal transmissionresource from a pool), a signal format (e.g., number of symbols occupiedby a D2D signal in a subframe, number of subframes used for transmittinga D2D signal), signal strength from an eNB, strength of transmit powerof a D2D UE, and the like. For clarity, a method for an eNB to directlydesignate a transmission resource of a D2D transmission UE is referredto as a mode 1. If a transmission resource region is configured inadvance or an eNB designates the transmission resource region and a UEdirectly selects a transmission resource from the transmission resourceregion, it is referred to as a mode 2. In case of performing D2Ddiscovery, if an eNB directly indicates a resource, it is referred to asa type 2. If a UE directly selects a transmission resource from apredetermined resource region or a resource region indicated by the eNB,it is referred to as a type 1.

Transmission and Reception of SA

A mode 1 UE can transmit an SA signal (or, a D2D control signal, SCI(sidelink control information)) via a resource configured by an eNB. Amode 2 UE receives a configured resource to be used for D2Dtransmission. The mode 2 UE can transmit SA by selecting a timefrequency resource from the configured resource.

The SA period can be defined as FIG. 9. Referring to FIG. 9, a first SAperiod can start at a subframe apart from a specific system frame asmuch as a prescribed offset (SAOffsetlndicator) indicated by higherlayer signaling. Each SA period can include an SA resource pool and asubframe pool for transmitting D2D data. The SA resource pool caninclude subframes ranging from a first subframe of an SA period to thelast subframe among subframes indicated by a subframe bitmap(saSubframeBitmap) to transmit SA. In case of mode 1, T-RPT(time-resource pattern for transmission) is applied to the resource poolfor transmitting D2D data to determine a subframe in which an actualdata is transmitted. As shown in the drawing, if the number of subframesincluded in an SA period except the SA resource pool is greater than thenumber of T-RPT bits, the T-RPT can be repeatedly applied and the lastlyapplied T-RPT can be applied in a manner of being truncated as many asthe number of remaining subframes. A transmission terminal performstransmission at a position of which a T-RPT bitmap corresponds to 1 inan indicated T-RPT. One MAC PDU performs transmission four times.

In the aforementioned V2V communication corresponding to communicationperformed between vehicle terminals, it may use 5.9 GHz band. Afrequency offset may considerably occur in a high frequency band such as5.9 GHz and the like. Moreover, since mobility is high due to thecharacteristic of a vehicle, it is highly probable that a frequencyerror occurs due to the Doppler shift. In particular, in case ofperforming the V2V communication, due to the specificity ofcommunication environment of the V2V communication, it may be difficultto guarantee synchronization performance of an optimum level. Hence, amethod of generating and/or transmitting a synchronization signalcapable of showing good performance even in such communicationenvironment as a high carrier frequency, high mobility, and the like. Inthe following description, a synchronization signal for V2V, V2X, andthe like is commonly referred to as a V-SS. Although a method ofgenerating/transmitting the V-SS is explained centering on a UE, themethod can also be applied to a V-SS generated/transmitted by a basestation. An SSSS (m-sequence based sequence) transmitted by a V-UE and aPSSS (Zadoff-Chu based sequence) are referred to as a VSSS (vehiclesecondary synchronization signal) and a VPSS (vehicle primarysynchronization signal), respectively.

Embodiment 1

A first embodiment is to transmit a sequence with subcarrier spacingselected from among 1, 2, 4, 8, and 16 multiples of 15 kHz (i.e., 15KHz, 30 KHz, 60 KHz, 120 KHz, and 240 KHz) in frequency domain. Thefirst embodiment can be comprehended as a scheme of transmitting an SLSS(PSSS and/or SSSS) of legacy 6 RBs by configuring the SLSS with a combrepetition factor 2, 4, 6, or 16. Yet, a value of the repetition factoris just an example. The comb repetition factor is not restricted to asquare of 2. It may also use a repetition factor of a natural number.

Specifically, the abovementioned method can be implemented in a mannerthat a NULL subcarrier is inserted between sequences (elements) (of anSLSS). In frequency domain, if a NULL subcarrier is inserted betweensequence elements, it may have an effect that subcarrier spacing iseffectively widened. In this case, a form of inserting the NULLsubcarrier may vary depending on whether a waveform used for V-SScorresponds to OFDM or SC-FDM. And, the form of inserting the NULLsubcarrier may vary depending on a repetition factor. In case of usingthe SC-FDM, since there is no DC subcarrier, NULL can be evenly filledfor a comb patterned. On the contrary, in case of using the OFDM, sincethere is a DC subcarrier, if a NULL subcarrier is simply insertedbetween elements of a sequence, the elements become asymmetrical on thebasis of the DC. As a result, it is unable to use a legacy detector. Inorder to solve the problem, it may use a method of generating and/ortransmitting a (synchronization) sequence described in the following.For example, in case of using an OFDM waveform, a synchronization signalto RE mapping method of a comb type can be expressed by an equationdescribed in the following.

$\begin{matrix}{{{a_{k,l} = {d(n)}},\mspace{14mu} {n = 0},\ldots \mspace{14mu},30}{k = {n - 31 + \frac{N_{RB}^{DL}N_{sc}^{RB}}{2}}}{{a_{k,l} = {d(n)}},\mspace{14mu} {n = 31},\ldots \mspace{14mu},62}{k = {n - 30 + \frac{N_{RB}^{DL}N_{sc}^{RB}}{2}}}} & \left\lbrack {{Equation}\mspace{14mu} 12} \right\rbrack\end{matrix}$

In equation 12, d(n) coressponds to a sequence described in thefollowing, a_(k,l) corresponds to an RE to which the sequence is mapped,N_(RB) ^(DL) corresponds to a downlink bandwidth, and N_(sc) ^(RB)corresponds to an RB size of a subcarrier unit.

A base station or a UE generates a sequence of a length of 63 of whichthe center of the sequence is punctured (or, a sequence to which a nullis inserted), inserts one or more 0s between elements of the sequence,maps the sequence to an RE, and transmits the mapped sequence. In thiscase, the number of one or more 0s inserted between elements of thesequence corresponds to (repetition factor—1). If the repetition factorcorresponds to an even number, it may be able to additionally insert 0sto make symmetry on the basis of the center element (i.e., DCsubcarrier) of the sequence. In this case, the number of additionallyinserted 0s may correspond to (repetition factor—1). The abovementionedmethod of generating and mapping the sequence can also be performedusing a method described in the following. The base station or the UEgenerates a first sequence of a length of 63 of which the center of thesequence is punctured (or, a sequence to which a null is inserted) andmay be able to generate a second sequence by inserting one or more 0sbetween elements of the sequence. In this case, the number of one ormore 0s inserted between elements of the first sequence corresponds to(repetition factor—1). If the repetition factor corresponds to an evennumber, it may be able to additionally insert 0s to make symmetry on thebasis of the center element (i.e., DC subcarrier) of the first sequence.In this case, the number of additionally inserted 0s may correspond to(repetition factor—1). The base station or the UE maps the generatedsecond sequence to an RE and may be able to transmit the mappedsequence.

FIG. 10 illustrates a case of simply inserting 0s when a repetitionfactor corresponds to 2 (case 1) and a case of additionally inserting 0son the basis of a DC subcarrier (case 2). FIG. 11 illustrates exampleswhen a repetition count corresponds to 4. Specifically, when 0s aresimply inserted (case 1), it may add a NULL subcarrier to a positionnear DC (case 2). If a NULL subcarrier is removed (case 3), it may addNULLs as many as (repetition factor—1) to a position near DC (case 4).In each of the cases, if the number of additionally inserted 0scorresponds to (repetition factor—1), in particular, if 3 0s areadditionally inserted, it may be able to maintain the same intervalspacing between subcarriers to which a sequence is mapped whilesymmetrical characteristic is maintained on the basis of a DCsubcarrier. If the same interval is maintained between subcarriers towhich the sequence is mapped, it may be able to overcome a demeritincapable of using a legacy PSS detector in the cases 2 and 3.

When a repetition factor corresponds to an odd number, it may also beable to additionally insert 0s to make symmetry on the basis of thecenter element of a sequence. If the repetition factor corresponds tothe odd number, it may simply insert the (repletion factor—1) number of0s between elements of the sequence. In this case, in order to maintainthe time domain characteristic of a legacy PSS, it may add NULL to aposition near a DC subcarrier. FIG. 12 illustrates an example of theabovementioned method.

Meanwhile, if it is unable to reuse a legacy PSS detector, it can becomprehended as a sequence form distinguished from a PSS. Hence, if itis designed to distinguish the PSS from V-SS, it can be utilized as amerit rather than a demerit. In particular, if a time domain sequence ofa form different from a form of the PSS is intentionally generated, thetime domain sequence can be distinguished from the legacy PSS. In thiscase, a repetition factor of a PSSS can be configured in a manner ofbeing different from a repetition factor of an SSSS. (If the SSSS istransmitted from the V-SS), when an ID of a synchronization source isidentified using the SSSS after time/frequency synchronization ismatched via the PSSS, a size of frequency domain occupied by the SSSScan be reduced to use an RE in transmitting other data. If a sequenceidentical to the legacy SLSS is transmitted using a repetition factorequal to or greater than 2, a legacy SLSS sequence appears in a repeatedform in time domain. If the legacy SLSS is transmitted during 6 RBs, asa repetition factor (x) is getting bigger, a bandwidth on which asynchronization for V2X is transmitted may become 6*RB. According to theabovementioned method, since it is able to repetitively implement anSLSS used in legacy D2D in time domain, it may be able to reduceimplementation complexity in a legacy UE. Moreover, since it is able tohave wide subcarrier spacing in frequency domain, it is able to detect asynchronization signal even when there is a high frequency error. Sinceit is able to have a form that the same sequences are repeated in oneOFDM symbol, the same sequences can estimate a high frequency error inthe symbol via correlation when a frequency offset occurs.

Embodiment 2

A second embodiment is to repetitively configure a sequence in frequencydomain. The number of repeating frequency domain can be determined inadvance or can be signaled using one of methods defined in legacy LTE.FIG. 13 (a) illustrates a case of mapping a sequence in OFDM and FIG. 13(b) illustrates a case of mapping a sequence in SC-FDM. In case of theSC-FDM, since there is no DC subcarrier, the number of subcarrierscorresponds to 62. In case of the OFDM, 63 subcarriers (including DC)are effectively occupied. In case of using the OFDM scheme, it isnecessary for a signal repeated in frequency domain to satisfy twoproperties including left/right symmetry on the basis of a DC subcarrierand repetition of the same sequence in frequency domain. In this case, asynchronization signal repeated in frequency domain may have a form that0 is padded between samples in the domain. This can be usefully used forestimating a timing offset in time domain.

In order to satisfy the two properties, it is necessary to delicatelyadjust a NULL subcarrier position on the basis of DC in the OFDM-basedscheme. Specifically, as shown in FIG. 14 (a), when a synchronizationsignal is repeated in frequency domain, a sequence repeated in the leftside on the basis of DC deploys a guard RE of 4 REs to a close side onthe basis of DC, deploys a guard RE of 5 REs to a far side on the basisof the DC, and deploys a NULL RE to the center of the sequence (originalDC position). Or, as shown in FIG. 14 (b), when a synchronization signalis repeated in frequency domain, a sequence repeated in the left side onthe basis of DC deploys a guard RE of 5 REs to a close side on the basisof DC, deploys a guard RE of 4 REs to a far side on the basis of the DC,and deploys a NULL RE to the center of the sequence (original DCposition). In the abovementioned two methods, although it is able toinsert NULL (zero gain) to an RE (a NULL subcarrier 1410 positioned atthe center of the repeated sequence in FIG. 14) positioned at theoriginal DC position of the repeated sequence, the RE can also be filledwith a unit gain (1) or a gain assigned to a DC subcarrier.

In case of using a waveform of the SC FDM, since there is no DC, thesame sequence (left/right 5 NULL REs) can be repeated in frequencydomain.

In the aforementioned method, a repetition count of a PSS constructing aV-SS may be different from a repetition count of an SSS. The repetitioncount can be determined in advance or can be configured by a network.Or, when a specific condition is satisfied by a UE, a repetition countof frequency domain can be determined and transmitted/received. If therepetition count is configured by the network or is determined by theUE, it may use all or a part of methods described in the following. Inthe meantime, the embodiment 2 can be used in a manner of beingindependent from the embodiment 1. Or, the embodiment 2 can be usedtogether with the embodiment 1. In particular, when repetition isperformed in frequency domain, the repetition can be performed in amanner of being extended to a comb form.

In the embodiment 1 and the embodiment 2, a sequence may correspond toeither a Zadoff-Chu sequence or an m-sequence. In particular, thesequence may correspond to a sequence for a PSS or a sequence for an SSSin legacy LTE. Or, the sequence may correspond to an SLSS sequence. Inparticular, a sequence can be used for acquiring synchronization by aV2X terminal which has received the sequence.

Although it is able to use the abovementioned description for V2X, thedescription can also be used for transmitting a wideband preamble or asynchronization signal in a different communication (e.g., LTEcommunication performed on an unlicensed band). And, a sequence mayindicate that a UE, which has transmitted the sequence, corresponds toan LTE UE. When LTE communication is performed on an unlicensed band, itmay correspond to communication performed with a UE performing adifferent communication scheme (e.g., 802.11 system). In particular, theabovementioned description can be used for performing communication witha device of a different communication scheme. In this case, although thecommunication is used for transmitting and receiving a signal with eachother, the communication can also be used for transmitting and receivinga specific signal to check the existence of a partner device. Inparticular, UEs of a different communication scheme are able to knowwhether or not an LTE UE exist based on a synchronization signalconfiguration scheme proposed in the present invention. Thesynchronization signal configuration scheme can be differentlyconfigured depending on a band or an LTE service. To this end, the UEsof the different communication scheme can be equipped with a device, acircuit, or a module for detecting all or a part of synchronizationsignals proposed by the present invention.

Meanwhile, in the embodiments 1 and 2, it may also consider a method oftransmitting a full band (a method of filling a full band with the samesequence or a method of filling a full band by inserting null betweenREs). When a synchronization signal is transmitted, if the remaining REis not used by a different UE, it may be able to enhance resolution intime domain by transmitting a full band.

Embodiments Related to Repetition Factor

Following description relates to a method of configuring the repetitionfactor mentioned earlier in the embodiments 1 and 2.

A repetition factor is configured by a network or can be differentlyconfigured according to mobility of a UE. In this case, a repetitionfactor of V-SS can be differently configured according to a resourceregion in which the V-SS is transmitted. For example, a repetitionfactor can be configured in proportion to a moving speed of a UE. If theUE moves with a speed equal to or greater than a prescribed threshold,it may configure a repetition factor of V-SS to be big to make therepetition factor robust to a frequency shift due to the Doppler Effect.As a different example, if an RSU or an eNB positioned on a road knowsor estimates an average moving speed of the road, the RSU or the eNBconfigures a repetition factor of V-SS on the road and signals therepetition factor to a vehicle UE (V-UE) or a pedestrian UE (P-UE) viaphysical layer signaling or higher layer signaling. Having received therepetition factor, the V-UE or the P-UE can perform atransmission/reception operation of the V-SS in consideration of thesignaled repetition factor.

A repetition factor can be configured according to a frequency of acarrier on which a sequence is transmitted. In particular, a repetitionfactor of a V-SS transmitted by a V-UE can be differently configuredaccording to a carrier frequency on which the V-SS is transmitted. Forexample, when a V-SS is transmitted on 5.9 GHz, the V-SS is transmittedby configuring a repetition factor with a big value. On the contrary,when a V-SS is transmitted on an LTE carrier equal to or narrower than 3GHz, the V-SS can be transmitted by configuring a repetition factor witha small value. Since a frequency error requirement is configured in aunit of PPM on the basis of a carrier frequency, if the carrierfrequency is big, an absolute frequency offset increases. Hence, if arepetition factor is configured to big on a carrier of a high frequencyband, it may be able to effectively handle the increase of the frequencyoffset.

It may be able to differently configure all or a part of IDs of a rootsequence/SSSS of a repetition factor/PSSS according to a type of a UEtransmitting or receiving a V-SS. For example, when a P-UE transmits aV-SS, a repetition factor transmitted by the P-UE can be configured tobe smaller than a repetition factor transmitted by a V-UE. This isbecause, since mobility of the P-UE is not that big, Doppler shiftoccurs less frequently between V-UEs. Or, if a UE receiving a V-SScorresponds to a P-UE (when a V-UE transmits a V-SS for a P-UE, aposition of a subframe in which the V-SS is transmitted can be signaledto the P-UE and the V-UE or can be determined in advance.), a repetitionfactor can be configured to be smaller than the V-SS transmitted to theV-UE. As an extreme case, when a V-UE performs transmission for a P-UE,the V-UE can perform the transmission using a repetition factoridentical to an SLSS.

In a V-SS, similar to an SLSS, an SSSS is not transmitted, the verylimited number of SSSS is transmitted, or an SSSS of a sequencedifferent from a sequence of an SLSS can be used. Basically, since aV-UE matches synchronization with a GPS, it is highly probable that mostof V-UEs have the same timing. In particular, since a separatesynchronization cluster is generated, the necessity for identifying thesynchronization cluster is reduced. As a result, the number of SSSS isreduced or the SSSS is not transmitted. For example, a VSSS used by aV-UE may use a scheme of performing transmission in a 5th subframe in anSSS (secondary synchronization signal) used in LTE. This is because,since an SSS of an SLSS uses an SSS of a 0th subframe, it is necessaryto distinguish the SSS from a sequence used in the SLSS. For the similarreason, the PSSS may also use a single root sequence only. If multiplePSSSs are used, it may be able to configure a root sequence of the PSSSsto be differently used according to whether or not a GPS synchronizationsignal is successfully received. For example, if V-UEs successfullymatch synchronization with a GPS, the V-UEs may use a root sequence A.If UEs fail to match synchronization with the GPS, it may determine arule that the UEs use (transmit) a PSSS of a root sequence B. Theabovementioned embodiments can be determined in advance or can bedifferently configured according to a carrier frequency on which a V-SSis transmitted. If SSSS is not transmitted, a corresponding RE can beused by PSBCH. If the SSSS is used, it may perform rate matching on aposition of the SSSS.

In V-SS, it may or may not transmit PSBCH. If the PSBCH is transmitted,it may be able to define PSBCH of a new format. If a legacy PSBCH isreused, a partial field of the legacy PSBCH can be used as a virtual CRCwithout being used. For example, among the fields of the PSBCH, a TDDconfiguration field and a bandwidth field may not be used for a V2Xdedicated carrier. In case of a DFN (D2D frame number) field, if a GPSreceived UE assumes that a clock drift is not big, the DFN field may notbe used. If a V-SS is transmitted to a UE, which has fails to receive aGPS, the DFN can be transmitted via the PSBCH. This scheme helps the UE,which has failed to receive a GPS, to receive a V-SS and configure theDFN.

A repetition factor can be configured according to whether or not a UEreceiving a sequence is connected with a GPS. All or a part of arepetition factor, a root sequence of a PSSS, and an ID of an SSS can bedifferently configured according to whether or not a GPS signal issuccessfully received or an assumption that a UE fails to receive a GPSsignal. And, an SLSS ID represented by a combination of the rootsequence of the PSSS and the ID of the SSSS can be differentlyconfigured for UEs, which have successfully receives a GPS signal, orUEs using the GPS as a reference of time synchronization. For example, aspecific SLSS ID can be determined in advance or can be signaled by anetwork for the UEs. If it is assumed that frequency synchronization ofthe GPS is used for transmitting and receiving a V-SS, a frequencyoffset may differently occurs according to whether or not the GPS isconnected. Yet, since the frequency offset corresponds to a relativething between UEs, if either a Tx UE or an Rx UE fails to receive GPS,it is necessary to consider a possibility that the frequency offsetincreases. In particular, although the Tx UE is connected with the GPS,if a UE receiving a V-SS transmitted by the Tx UE corresponds to a UE,which has failed to connect to the GPS (or, if it is able to estimatethat the UE is not connected with the GPS), it may configure arepetition factor to be big and transmit the repetition factor.

All or a part of the proposed schemes can be applied not only to a V-SSbut also to an RS transmitted by a V-UE. For example, it may be able todifferently configure a repetition factor of an RS and/or data accordingto a carrier on which the RS is transmitted, mobility/lane/heading, or atype of a Tx/Rx UE.

Examples for the aforementioned proposed methods can also be included asone of implementation methods of the present invention. Hence, it isapparent that the examples are regarded as a sort of proposed schemes.The aforementioned proposed schemes can be independently implemented orcan be implemented in a combined (aggregated) form of a part of theproposed schemes. It may be able to configure an eNB to inform a UE ofinformation on whether to apply the proposed methods (information onrules of the proposed methods) via a predefined signal (e.g., physicallayer signal or upper layer signal).

Configurations of Devices for Embodiments of the Present Invention

FIG. 15 is a diagram for configurations of a transmitter and a receiver.

Referring to FIG. 15, a transmit point apparatus 10 may include areceive module 11, a transmit module 12, a processor 13, a memory 14,and a plurality of antennas 15. The antennas 15 represent the transmitpoint apparatus that supports MIMO transmission and reception. Thereceive module 11 may receive various signals, data and information froma UE on an uplink. The transmit module 12 may transmit various signals,data and information to a UE on a downlink. The processor 13 may controloverall operation of the transmit point apparatus 10.

The processor 13 of the transmit point apparatus 10 according to oneembodiment of the present invention may perform processes necessary forthe embodiments described above.

Additionally, the processor 13 of the transmit point apparatus 10 mayfunction to operationally process information received by the transmitpoint apparatus 10 or information to be transmitted from the transmitpoint apparatus 10, and the memory 14, which may be replaced with anelement such as a buffer (not shown), may store the processedinformation for a predetermined time.

Referring to FIG. 15, a UE 20 may include a receive module 21, atransmit module 22, a processor 23, a memory 24, and a plurality ofantennas 25. The antennas 25 represent the UE that supports MIMOtransmission and reception. The receive module 21 may receive varioussignals, data and information from an eNB on a downlink. The transmitmodule 22 may transmit various signals, data and information to an eNBon an uplink. The processor 23 may control overall operation of the UE20.

The processor 23 of the UE 20 according to one embodiment of the presentinvention may perform processes necessary for the embodiments describedabove.

Additionally, the processor 23 of the UE 20 may function tooperationally process information received by the UE 20 or informationto be transmitted from the UE 20, and the memory 24, which may bereplaced with an element such as a buffer (not shown), may store theprocessed information for a predetermined time.

The configurations of the transmit point apparatus and the UE asdescribed above may be implemented such that the above-describedembodiments can be independently applied or two or more thereof can besimultaneously applied, and description of redundant parts is omittedfor clarity.

Description of the transmit point apparatus 10 in FIG. 15 may be equallyapplied to a relay as a downlink transmitter or an uplink receiver, anddescription of the UE 20 may be equally applied to a relay as a downlinkreceiver or an uplink transmitter.

The embodiments of the present invention may be implemented throughvarious means, for example, hardware, firmware, software, or acombination thereof.

When implemented as hardware, a method according to embodiments of thepresent invention may be embodied as one or more application specificintegrated circuits (ASICs), one or more digital signal processors(DSPs), one or more digital signal processing devices (DSPDs), one ormore programmable logic devices (PLDs), one or more field programmablegate arrays (FPGAs), a processor, a controller, a microcontroller, amicroprocessor, etc.

When implemented as firmware or software, a method according toembodiments of the present invention may be embodied as a module, aprocedure, or a function that performs the functions or operationsdescribed above. Software code may be stored in a memory unit andexecuted by a processor. The memory unit is located at the interior orexterior of the processor and may transmit and receive data to and fromthe processor via various known means.

Preferred embodiments of the present invention have been described indetail above to allow those skilled in the art to implement and practicethe present invention. Although the preferred embodiments of the presentinvention have been described above, those skilled in the art willappreciate that various modifications and variations can be made in thepresent invention without departing from the spirit or scope of theinvention. For example, those skilled in the art may use a combinationof elements set forth in the above-described embodiments. Thus, thepresent invention is not intended to be limited to the embodimentsdescribed herein, but is intended to accord with the widest scopecorresponding to the principles and novel features disclosed herein.

The present invention may be carried out in other specific ways thanthose set forth herein without departing from the spirit and essentialcharacteristics of the present invention. Therefore, the aboveembodiments should be construed in all aspects as illustrative and notrestrictive. The scope of the invention should be determined by theappended claims and their legal equivalents, and all changes comingwithin the meaning and equivalency range of the appended claims areintended to be embraced therein. The present invention is not intendedto be limited to the embodiments described herein, but is intended toaccord with the widest scope consistent with the principles and novelfeatures disclosed herein. In addition, claims that are not explicitlycited in each other in the appended claims may be presented incombination as an embodiment of the present invention or included as anew claim by subsequent amendment after the application is filed.

INDUSTRIAL APPLICABILITY

The embodiments of the present invention can be applied to variousmobile communication systems.

1.-12. (canceled)
 13. A method of transmitting a synchronization signalin a wireless communication system, comprising the steps of: generatinga secondary synchronization signal; and transmitting the generatedsecondary synchronization signal, wherein the secondary synchronizationsignal is transmitted only in subframe 5 among subframe 0 to subframe 9,when the secondary synchronization signal is transmitted by a V-UE(vehicle UE).
 14. The method of claim 13, wherein secondarysynchronization signal is transmitted only in subframe 0 among subframe0 to subframe 9, when the secondary synchronization signal istransmitted by a D2D(Device-to-Device) UE.
 15. A user equipment (UE)transmitting a synchronization signal in a wireless communicationsystem, comprising: a transmitter and a receiver; and a processor, theprocessor configured to generate a secondary synchronization signal, theprocessor configured to transmit the generated secondary synchronizationsignal, wherein the secondary synchronization signal is transmitted onlyin subframe 5 among subframe 0 to subframe 9, when the secondarysynchronization signal is transmitted by a V-UE (vehicle UE).